Can't Keep Loop Cut & Slide Where I Want With Measurements
The loop cut tool or Loop Subdivide as it may be called, is a two step tool that subdivides the chosen edge loop and then starts an Edge Slide.

In the first stage you can use the  MW or numpad-/+ to increase/decrease the number of cuts being made. You can also press E to keep a single loop parallel to the next edge loop and F will flip that to the other side.

In the second stage you are sliding the new edge loop/s along the edge that you are subdividing, the value you enter is a factor relative to the edge being cut with 0.0 being in the centre and 1.0/-1.0 moving the new edge loop to either end of the edge being cut.

For more precise placement of vertices you want to use other tools that allow movement based on global position. The snapping tools make it easy to align items to each other.

When moving vertices and objects you can restrict movement to an axis and enter a distance to move. eg GX0.5 will move the selection 0.5 units on the x axis.

In the mesh display panel which can be found in the properties region N of the 3DView you can display the length of selected edges while editing.



The scene settings allow all sizes to be shown using metric or imperial units rather than an arbitrary unit.



As you are modelling buildings you might be interested in the Archimesh addon which you can download here - this addon has recently been added to the standard addons and will be included in the 2.78 release.